Robby Vroemans

Flow systems are considered as a promising solution for practical applications of light-driven reactions. Design and optimization of the reaction devices based on the characteristics of reaction types is important to achieve a full utilization of incident light and active sites of the photocatalysts, thereby achieving amplification of photocatalytic reactions.

Abstract

Photocatalytic synthesis of value-added chemicals has gained increasing attention in recent years owing to its versatility in driving many important reactions under ambient conditions. Selective hydrogenation, oxidation, coupling, and halogenation with a high conversion of the reactants have been realized using designed photocatalysts in batch reactors with small volumes at a laboratory scale; however, scaling-up remains a critical challenge due to inefficient utilization of incident light and active sites of the photocatalysts, resulting in poor catalytic performance that hinders its practical applications. Flow systems are considered one of the solutions for practical applications of light-driven reactions and have experienced great success in photolytic and homogeneous photocatalysis, yet their applications in heterogeneous photocatalysis are still under development. In this perspective, we have summarized recent progress in photolytic and photocatalytic synthetic chemistry performed in flow systems from the view of reactor design with a special focus on heterogeneous photocatalysis. The advantages and limitations of different flow systems, as well as some practical considerations of design strategies are discussed.

Biomass-derived feedstocks for hydrogen production are crucial as an alternative to fossil fuel especially in those areas where green electricity and clean water are scarce. In this framework the transformation of simple (formic acid, alcohols) and more complex (polyalcohols, sugars and cellulose) bio-derivatives in pure hydrogen is recognized as a promising approach. Parallel to great effort in heterogeneous catalysis, milder molecular systems represent a more selective eye for alternative solutions and mechanistic insights. In the present review the introduction summarizes the challenges in the catalytic utilization of biomass-derived feedstocks, followed by the advances in homogeneously catalyzed hydrogen production from different substrates which will cover formic acid, with oustanding efficiency with noble metals and promising results with earth abundant ones and alcohols and polyalcohols, with particular emphasis to the development of heterogenized systems, ligand assisted catalysts and bi-catalytic synergistic solutions which allow to avoid base and to promote catalyst stability and recyclability. In the last part, description of hydrogen production from more complex substrates, such as sugars and cellulose, will show the role of molecular complexes in main and side reactions. Critical comments on the reported advances are provided along the whole discussion.

Synlett
DOI: 10.1055/a-2293-3243

Herein, we present a rapid and efficient method for synthesizing cyclic acetals and ketals utilizing a rotary evaporator. Unlike the conventional Dean–Stark dehydration process, which typically demands extended reaction times and copious amounts of organic solvents, our approach affords the synthesis of cyclic acetals and ketals with varying ring sizes in 30 min while using minimal quantities of dimethyl sulfoxide as the solvent. This innovative protocol features high yields, fast reactions, easy operation, and broad substrate applicability.
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Article in Thieme eJournals:
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Catalysts, Vol. 14, Pages 250: Diphenyl Carbonate: Recent Progress on Its Catalytic Synthesis by Transesterification

Catalysts doi: 10.3390/catal14040250

Authors: Dong Wang Feng Shi Guochao Yang

Diphenyl carbonate is one of the raw materials used for the synthesis of polycarbonate, and its green and clean production is of great importance to the non-phosgene process for polycarbonate. The production of diphenyl carbonate by transesterification is its representative process route and is considered to be one of the typical examples of a green and sustainable process for chemicals. Since the discovery of the transesterification catalyst for diphenyl carbonate in the 1970s, researchers have been committed to improving its catalytic activity and selectivity and, correspondingly, the reaction engineering process. However, thermodynamic limitations, low activity, low selectivity, and limited stability have been bottlenecks that the transesterification catalyst has not been able to completely overcome, and the improvement of the catalyst is still ongoing. Therefore, this review takes the transesterification reaction of dimethyl carbonate and phenol as a model reaction and, based on a review of the progress in catalyst research on catalytic reaction processes, tries to clarify the structure–activity relationship between catalytic active sites and catalytic performance in homogeneous and heterogeneous catalytic processes and provides an overview of the progress in catalyst synthesis and modification.

Nature Chemistry, Published online: 28 March 2024; doi:10.1038/s41557-024-01470-8

Nature Synthesis, Published online: 27 March 2024; doi:10.1038/s44160-024-00515-7

An intramolecular electrochemical dehydration reaction of dicarboxylic acids to their cyclic anhydrides is presented. This electrolysis allows dicarboxylic acids as naturally abundant, inexpensive, safe, and readily available starting materials to be transformed into carboxylic anhydrides under mild reaction conditions. No conventional dehydration reagent is required. The obtained cyclic anhydrides are highly valuable reagents in organic synthesis, and in this report, we use them in-situ for acylation reactions of amines to synthesize amides. This work is part of the recent progress in electrochemical dehydration, which – in contrast to electrochemical dehydrogenative reactions for example – is an underexplored field of research. The reaction mechanism was investigated by 18O isotope labelling, revealing the formation of sulfate by electrochemical oxidation and hydrolysis of the thiocyanate supporting electrolyte. This transformation is not a classical Kolbe-electrolysis, because it is non-decarboxylative, and all carbon atoms of the carboxylic acid starting material are contained in the carboxylic anhydride. In total, 20 examples are shown with NMR yields up to 71%.

Nature Synthesis, Published online: 26 March 2024; doi:10.1038/s44160-024-00499-4

Publication date: 15 April 2024

Source: Molecular Catalysis, Volume 559

Author(s): Jie Xu, Qiqi Li, Tianlin Ma, Yujie Wang

Publication date: 15 June 2024

Source: Coordination Chemistry Reviews, Volume 509

Author(s): Sem Bleus, Wim Dehaen